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Can a fake fir tell the truth about Swiss needle cast? (paper)
Citation:
Lee, EHenry, P. Beedlow, Ron Waschmann, S. Cline, Mike Bollman, C. Wickham, AND N. Testa. Can a fake fir tell the truth about Swiss needle cast? (paper). In Proceedings, Swiss Needle Cast Coop 2015 Annual Meeting, Corvallis, OR, December 01, 2015. Oregon State University, Corvallis, OR, 45-54, (2016).
Impact/Purpose:
By the end of the 21st century, climate models predict hotter, drier summers and warmer, wetter winters in the Pacific Northwest (PNW), resulting in decreased snowpack, earlier snowmelt, and increased summer water balance deficit. These changes are already affecting sensitive forested ecosystems, raising concerns that forests are becoming increasingly susceptible to tree pathogens, phytophagous insects, and fires. Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) is a dominant PNW tree species that is infected by the foliar fungus Phaecryptopus gaeumannii (Rhode) Petrak which causes Swiss needle cast (SNC) disease. Very little is known about the history and geographic extent of SNC impacts. WED scientists developed a conceptual model of SNC impacts on Douglas-fir growth that characterizes the unique sinusoidal behavior of the causal fungus P. gaeumannii and its effects on tree growth. WED scientists were first to show that SNC is an ancient forest disease that can be traced back in time to ~65,000 radioactive years Before Present which is the earliest record of Douglas-fir presence in the PNW. Our work is important for filling in the gaps of knowledge in understanding the complex interactions of climate and biotic disturbance agents on tree growth in the PNW under climate change scenarios. As temperature rises and summer droughts intensity, Douglas-fir will likely experience greater temperature, water, and forest disturbance outbreak events, resulting in decreased forest health and condition.
Description:
A key question in dendrochronology to reconstruct forest disturbance history is how to distinguish between the effects of Swiss needle cast (SNC) and other forest disturbance agents (e.g., Arceuthobium spp., Armillaria, Phaseolus schweinitzii, Dendroctonus ponderosae, Dendroctonus pseudotsugae, Choristoneura occidentalis Freeman, Orgyia pseudotsugata McDunnough) on radial stem growth of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). SNC impacts physiological processes of carbon and water relations by stomatal occlusion and early needle abscission resulting in a reduction of tree growth with a distinct periodicity, whereas phytophagous pests reduce tree growth by defoliation with epidemics following less regular pseudo-periodicities. Outbreaks of the various forest disturbance agents differ in their magnitude, frequency, and duration. In particular, SNC impacts on Douglas-fir growth display a primary periodicity of 6-30 years and a secondary periodicity of 3-5 years which is unique to the causal fungus Phaeocryptopus gaeumannii (Rhode) Petrak. We use frequency domain analysis of tree-ring chronologies of Douglas-fir to identify the SNC disease cycle and separate the confounding effects of climate and SNC. We demonstrate the dendroecological reconstruction of SNC impacts on ancient Douglas-fir trees dated ~65K radioactive years B.P. from Eddyville, OR that were unearthed by the Oregon Department of Transportation.
